Here is 20" Armalite Ar Flattop Upper for $550 obo.
It is a 1:9 twist flat top with BCG & CH. Also comes with Carry Handle.
It also has Cali legal YHM muzzle break on it.
I am the original owner bought new and shot 200 rounds through it.
Very Accurate, never gave me any problems.
I am in Socal OC area and Let me know what you think.
I am also open for trade with 16" upper(equal quality)